Intelligent lighting has become widespread, and RF communication is a powerful technology to be used in the tele management of lamps, in particular for domestic and office environments. Instead of controlling the power, e.g. 230 V supply, to the lamp, the trend has moved towards directly controlling the light source or lighting device, i.e. the exchangeable element of the lamp, by sending an RF control signal to the lighting device. For indoor use the ISM band covers suitable frequencies to allow communication over a range of up to 20 meter. A suitable communication standard for low data-rate applications such as tele management of lamps is ZigBee. The transmitted control signals can be used to remotely control the state (ON/OFF), light-output (color, Luminous Flux), beam-width or orientation of the lamp. To effectively transmit or receive such tele management control signals, each lamp has to be provided with an antenna.
The performance of the antenna in a lamp must not be disturbed by other lamp components made from electrically conductive materials (or non-conductive materials that may lower the Q factor or resonance frequency) that could shield the RF signal in certain directions or change resonance frequency of the antenna, and thus significantly influence the RF communication with remote controls or other lamps. Thus, it is import that the antenna that radiates with significant directive gain in a large solid angle. For reliable communication with other lamps and with remote controls, the solid angle corresponding to all directions with sufficient gain (e.g. more than −10 dB with reference to an loss-less isotropic antenna) should practically be in the range between 2π and 3π. This is a problem to obtain within the limited dimensions of the outer enclosure of such device, since such dimensions are often dictated by standard size housings and power sockets.
US 2007/0252528 describes a lighting fixture or luminaire, such as used in street-lighting, incorporating an RF antenna. However, the RF antenna is placed outside the lighting device forming the light source, rather the RF antenna is placed in a portion of the external housing which is made of a non-shielding material that does not disturb RF waves in reaching the antenna.